Display device

ABSTRACT

A display device comprising at least one light modulation panel and at least two projection elements, wherein, in operation, an image having a relatively high resolution in a relatively small field of view is presented to a first eye by means of the first projection element, while an image having a relatively low resolution in a relatively large field of view is presented to a second eye by means of the second projection element. The second projection element is provided with means for masking a part of the large field of view, which part substantially corresponds to the small field of view.

[0001] The invention relates to a display device comprising at least oneline modulation panel and at least two projection elements, in which, inoperation, an image having a relatively high resolution in a relativelysmall field of view is presented to a first eye by means of the firstprojection element, while an image having a relatively low resolution ina relatively large field of view is presented to a second eye by meansof the second projection element.

[0002] In such a display device, which is known from U.S. Pat. No.5,912,650, an image having a relatively high resolution for a relativelysmall field of view or an image having a relatively low resolution for arelatively large field of view is alternately generated by means of thelight modulation panel. The display device is provided with means foralternately presenting the first or the second image to the first or thesecond eye. Thus, images having a relatively high resolution in arelatively small field of view are observed by one eye, while imageshaving a relatively low resolution in a relatively large field of vieware observed by the other eye.

[0003] The images presented to both eyes are combined in the human brainto an image having a relatively large field of view with a relativelylow resolution in which a relatively small field of view with arelatively high resolution is located.

[0004] The display device described in U.S. Pat. No. 5,912,650 has,however, a plurality of drawbacks. The light modulation panel is to becontrolled alternately for generating an image with a relatively highresolution in a relatively small field of view and for generating animage with a relatively low resolution in a relatively large field ofview. Consequently, the control of the light modulation panel isrelatively complicated. Moreover, also the part corresponding to thesmall field of view is illuminated by the second projection element,which part is replaced in the human brain by the image having arelatively high resolution and formed by means of the first projectionelement.

[0005] Consequently, an optimal illumination is not obtained.

[0006] It is an object of the invention to provide a display device inwhich images having a relatively low resolution in a relatively largefield of view are generated in a simple manner, while a relatively smallfield of view having a relatively high resolution is located in thelarge field of view.

[0007] In the display device according to the invention, this object isachieved in that the second projection element with the large field ofview is provided with means for masking a part of the large field ofview, which part substantially corresponds to the small field of view.

[0008] Since the part of the large field of view corresponding to thesmall field of view is masked by means of the second projection element,both projection elements can be optimized for the function to beperformed by the relevant projection elements, namely for generating animage with a relatively high resolution in a relatively small field ofview, or for generating an image with a relatively low resolution in arelatively large field of view, with one image being presented to oneeye and the other image being presented to the other eye.

[0009] An embodiment of the display device according to the invention ischaracterized in that each projection element is provided with aseparate light modulation panel in which the image for a relativelysmall field of view can be generated by means of the first lightmodulation panel, while the image for the relatively large field of viewcan be generated by means of the second light modulation panel.

[0010] In this way, images can be continuously presented to both eyes.

[0011] A further embodiment of a display device according to theinvention is characterized in that the second projection element isprovided with the light modulation panel, a lens preceding the lightmodulation panel, a concave mirror surrounding the light modulationpanel and a layer preceding the lens, which layer is reflective to lightbeams from the lens towards the concave mirror, said layer beingprovided with a masked part for masking the desired part of the largefield of view.

[0012] A relatively large field of view can be generated in a simplemanner by means of such a projection element which is provided with aconcave mirror. The part to be withdrawn from the large field of view iseffectively masked by the masked part provided on the layer.

[0013] Moreover, the masking prevents light rays from the lightmodulation panel from directly reaching the eye. These light rays do notcontribute to the formation of the image on the retina of the eye. Theydisturb the image. This is also referred to as stray light.

[0014] In principle, a 100% transmission for the light rays from thelight modulation panel to the pupil of the eye can be obtained by themasking effect.

[0015] These and other aspects of the invention are apparent from andwill be elucidated with reference to the embodiments describedhereinafter.

[0016] In the drawings:

[0017]FIG. 1 shows a projection element of a display device according tothe invention for generating an image with a relatively high resolutionin a relatively small field of view,

[0018]FIG. 2 shows a projection element of a display device according tothe invention for generating an image with a relatively low resolutionin a relatively large field of view.

[0019] In the Figures, corresponding components are denoted by the samereference numerals.

[0020]FIGS. 1 and 2 show projection elements 1, 2 of a display deviceaccording to the invention, which can be positioned on or around auser's head. The first projection element 1 can be positioned in frontof the first eye 3 of a user, while the second projection element 2 canbe positioned in front of the other, second eye 4 of the user.

[0021] The first projection element 1 is provided with a lightmodulation panel 5, an illumination unit 6 preceding the lightmodulation panel, two lenses 7, 8 preceding the illumination unit 6, anda cover glass 9 preceding the lenses 7, 8. The lenses 7, 8 image lightbeams 10 from the light modulation panel 5 in a relatively small viewingangle 11 of, for example, 40° with respect to the optical axis 12 of theprojection element 1.

[0022]FIG. 1 shows the radiation of only three pixels P1, P2, P3 of thelight modulation panel 5 to the pupil of the eye, a central pixel P2 andtwo pixels P1, P3 on the edge of the light modulation panel 5. Theradiation of each individual pixel P1 to P3 is shown by means of threerays, a central ray going from the center to the pupil of the eye andtwo rays going to the edge of the eye.

[0023]FIG. 2 shows the second projection element 2 which is providedwith a light modulation panel 13, an illumination unit 14 preceding thelight modulation panel 13, a lens 15 preceding the illumination unit 14,a masking ring 16 surrounding the lens 15, a concave mirror 17surrounding the masking ring 16, and a layer 18 preceding the lens 15.The layer 18 is provided with a masked part 19 which symmetricallysurrounds the optical axis 20 of the projection element 2.

[0024] The layer 18 is reflective to light beams from the lightmodulation panel 13 and transparent to the light beams from the concavemirror 17.

[0025] The layer 18 may be a semi-transmissive mirror, a mirror which issensitive to the direction of polarization, or a cholesteric mirror.

[0026] The projection element 2 operates as follows. Light beams 21 fromthe light modulation panel 13 are deflected by the lens 15 to a part ofthe layer 18 located outside the masked part 19. At this part of thelayer, the light beams 21 are reflected as light beams 22 towards theconcave mirror 17. The light beams 22 are subsequently reflected againas light beams 23 by the concave mirror 17 and subsequently pass throughthe layer 18 into the direction of the eye 4. Due to the deflectingeffect of the lens 15 as well as by the masked part 19 and the maskingring 16, it is prevented that a centrally located field of view 24 isilluminated. Consequently, only the field of view 25 surrounding thefield of view 24 is imaged on the eye 4 by means of the projectionelement 2. The viewing angle of the field of view 25 is, for example,40° to 96°.

[0027] The light modulation panel 13 generates an image of therelatively large field of view. A relatively low resolution is achievedby the relatively large field of view. Moreover, the rays of theprojection element 2 are imaged outside the central part of the retina.Here, the eye has also a smaller resolution and becomes increasinglysmaller as it is more remote from the blind spot. However, an image onthe high-resolution central part of the retina for the relatively smallfield of view is generated by means of the light modulation panel 5, sothat the image acquires a relatively high resolution. The images imagedon both eyes 3, 4 are combined in the human brain to a single image, inwhich a relatively large field of view with a relatively low resolutionis combined with a preferably centrally located small field of view witha relatively high resolution.

[0028] If layer 18 is provided with a cholesteric mirror, a λ/4 plate,which converts linearly polarized light into circularly polarized light,is arranged between the lens 15 and the layer 18.

[0029] If layer 18 is provided with a reflective polaroid, a λ/4 plateis arranged right in front of the concave mirror 17 so as to rotate thelinear direction of polarization through 90°.

1. A display device comprising at least one light modulation panel andat least two projection elements, in which, in operation, an imagehaving a relatively high resolution in a relatively small field of viewis presented to a first eye by means of the first projection element,while an image having a relatively low resolution in a relatively largefield of view is presented to a second eye by means of the secondprojection element, characterized in that the second projection elementwith the large field of view is provided with means for masking a partof the large field of view, which part substantially corresponds to thesmall field of view.
 2. A display device as claimed in claim 1,characterized in that each projection element is provided with aseparate light modulation panel in which the image for a relativelysmall field of view can be generated by means of the first lightmodulation panel, while the image for the relatively large field of viewcan be generated by means of the second light modulation panel.
 3. Adisplay device as claimed in claim 1 or 2, characterized in that thesecond projection element is provided with the light modulation panel, alens preceding the light modulation panel, a concave mirror surroundingthe light modulation panel and a layer preceding the lens, which layeris reflective to light beams from the lens towards the concave mirror,said layer being provided with a masked part for masking the desiredpart of the large field of view.
 4. A display device as claimed in claim3, characterized in that a masking ring surrounds the lens.
 5. A displaydevice as claimed in claim 3 or 4, characterized in that the layer is asemi-transmissive mirror, a reflective polaroid, apolarization-sensitive mirror or a cholesteric mirror.
 6. A displaydevice as claimed in claim 5, characterized in that a {fraction (1/4)}λlayer is arranged between the lens and the concave mirror, on the onehand, and the cholesteric mirror, on the other hand, by means of whichlayer linearly polarized light is convertible into circularly polarizedlight.
 7. A display device as claimed in claim 5, characterized in thata {fraction (1/4)}λ layer precedes the concave mirror, by means of whichlayer the linear direction of polarization is rotatable through 90°. 8.A display device as claimed in any one of the preceding claims,characterized in that the large field of view has a viewing angle whichis larger than approximately 40°, while the small field of view has aviewing angle which is smaller than approximately 40°, the viewingangles of the small field of view and the large field of view at leastadjoining each other.